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This bug appears to have been reported against 'rawhide' during the Fedora 19 development cycle.
Changing version to '19'.
(As we did not run this process for some time, it could affect also pre-Fedora 19 development
cycle bugs. We are very sorry. It will help us with cleanup during Fedora 19 End Of Life. Thank you.)
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After taking a look at UAX#29 and the Pango code, current behavior is following the Unicode standard unfortunately.
Here is the details how the text segmentation is decided in Pango according to the standard:
First, the character type for the above characters are:
U+0C15 OTHER LETTER
U+0C4D NON SPACING MARK
Pango is looking at the grapheme boundary rule to decide if a character should be deleted by backspace key. it's defined as following in UAX#29:
* Break at the start(GB1) and end(GB2) of text.
* Do not break between a CR and LF(GB3). Otherwise, break before(GB4) and after(GB5) controls.
* Do not break Hangul syllable sequences(GB6,GB7,GB8).
* Do not break between regional indicator symbols(GB8a).
* Do not break before extending characters(GB9).
Only for extended grapheme clusters:
* Do not break before SpacingMarks(GB9a), or after Prepend characters(GB9b).
* Otherwise, break everywhere.
According to the table 2 in UAX#29, non-spacing mark is categorized into Extend. so it doesn't break *before* U+0C4D. but no rules to not break *after* Extend.
At this point, there are no standard that the software can refers the material to prevent that behavior. maybe good to escalate this to Unicode.org then.